Replaceable toner cartridges are widely used in electrophotographic printers and copiers. Many such cartridges include the charging device, which may be a corona wire to generate ions or may be a charge roller or other contact charging member. The cartridges sold by the assignee of this invention for its Optra (trademark) and 4039 families of printers have a charge roller in the cartridge. Accordingly, that charge roller necessarily is replaced when the cartridge is replaced.
U.S. Pat. No. 5,365,315 to Baker et al, assigned to the assignee of this invention, locates its charge roller out of the cartridge, specifically in the lid, and thereby permits use of the same charge roller for the life of the machine. However, each charging operation entails some deterioration of the charge roller. With high printer usage and particularly with increased printing speeds, a single charge roller will not function for the life of the machine.
This invention places a charging device in the toner cartridge, but one which is a low-cost device suitable to charge the photoconductor to a level near the final charge required for printing. A charge roller in the printer or copier charges the precharged photoconductor to the final charge. Deterioration of the charge roller is greatly reduced such that the charge roller can last the life of a very heavy-duty printer (or other imaging apparatus).
U.S. Pat. No. 4,387,980 to Ueno et al discloses multiple, spaced contact charging members for the stated purpose of obtaining more uniform charging. This disclosure includes a three roller embodiment and a three brush embodiment. These are all commonly mounted in an imaging apparatus and not in a replaceable toner cartridge.